The present invention relates to array probes for non-destructive testing and inspection, and more particularly, to a flexibly eddy current or ultrasonic array probe assembly which can be applied and used to inspect contoured surfaces of varying cross-sectional geometry.
Any discussion of the related art throughout this specification should in no way be considered as an admission that such art is widely known or forms part of the common general knowledge in the field.
Although much of the discussion in the present disclosure speaks specifically to eddy current array probes, it is not limited in this regard. The flexible array probe of the present invention is well suited to any surface coupling array probe, such as, but not limited to, eddy current sensors, piezoelectric sensor elements—such as, but not limited to, ultrasonic transducers and bond testing probe elements—and magnetic flux leakage sensors—such as, but not limited to, Hall Effect sensor elements—devices.
Eddy current inspection is commonly used to detect flaws in manufactured components, such as tubes or billets. An inspection coil, typically referred to as an eddy current probe, is positioned near a piece to be inspected and driven with high frequency alternating electrical currents which, in turn, create an alternating magnetic field near the surface of the test piece. This magnetic field induces eddy currents in the conductive surface of the test piece which are sensed and measured by the eddy current probe. If a flaw or defect is present on the surface of the test piece, the flow of eddy currents will be altered, and this change will be readily detected by the eddy current probe. The amplitude and position of these current changes can then be analyzed and recorded, for example through visual inspection by a test operator or processed through an automated alarm algorithm, to determine the size and location of the defect or flaw. Eddy current array systems comprise of a plurality of inspection coils (or other types of eddy current sensors well known to those skilled in the art) arranged in such a way as to be conducive to a particular inspection task.
Eddy current inspection of contoured surfaces has long been a challenge in non-destructive testing and inspection. Some manufacturing processes—for example, billet rolling systems—can produce items with cross-sectional geometries defined only within a certain tolerance range. This variation on the shape of the test surface can make certain key aspects of eddy current inspection problematic. Maintaining a constant liftoff—the height at which an eddy current sensor is positioned above a test surface—for example can become extremely difficult using a solid, inflexible eddy current array probe. Similarly, it is critical that the axis of each eddy current sensor be held orthogonal to the surface under test. Using an eddy current array probe which holds its elements in fixed positions, this can be impossible to achieve while testing parts with varying geometry.
U.S. Pat. No. 4,543,528 to Baraona describes a flexible probe assembly which attempts to address these problems. Baraona's array probe uses a plurality of independent test heads—each housing at least one array element—fixed to each other with flexible bands. A two point coupling and alignment fixture—referred to as an “urging mechanism”—is also provided.
While Baraona's flexible array probe provides a reasonable solution to the problem of inspecting a convex surface, it holds a number of limitations. The range of motion (rotation) of each element in the array is limited by the rigidity of the flexible bands and by the spacing of the test heads. To achieve a useful probe curvature, array elements must either be spaced a distance apart or multiple elements placed on each test head. Both options significantly limit the usefulness of the flexible array probe. Baraona's probe and alignment fixture also make a poor showing of maintaining orthogonal coil orientation along sharply curved surfaces. Due to the nature of the design, each test head is allowed a degree of mobility against those directly adjacent to it, and the two point alignment fixture is not suited to support or align the critical center array elements. Furthermore, the design as presented is only suitable for testing convex surfaces.
Accordingly it would be advantageous to provide a robust flexible array probe which provides a large degree of flexibility while maintaining a tight element arrangement. Further, it would also be advantageous if the flexible array probe inherently tended to align its elements orthogonally to the surface of a structure under test. It would also be advantageous if the flexible array probe were conducive to measuring test pieces with variations in their cross-sectional geometry while maintaining a consistent eddy current sensor liftoff and orientation for every element in the array. It would further be advantageous if the probe were conducive to coupling to multiple curve shapes, including, but not limited to, convex, concave, and S-shaped surfaces.